The shape of the step-bending die is a complicated shape compared with a usual V bending die. The step-bending die is a special die individually designed so as to be adapted to product's shape and thickness. Namely, it was as shown in prior art FIGS. 4 and 5 in Japanese Published Unexamined Patent Application No. H0S-317972 A.
The step-bending die shown in FIG. 4 of the above-mentioned Patent Application is a fixed type for obtained step sizes, and FIG. 5 shows constitution which can vary the step sizes in order to obtain the step size by varying the number of spacers controlling position of an upper block and a lower block.